1. Field of the Invention
The present invention is in the field of optically readable, high storage density information carriers such as digital audio disks (CD) or video disks (VLP) containing improved reflective layers of alloys on that side of the information disk which contains the microstructure housing the recorded information. The reflective layer is itself covered with a protective layer.
2. Description of the Prior Art
In one method for manufacturing a disk-shaped information carrier, a blank is first manufactured in a transfer molding process. The information structure side of the blank is subsequently provided with the desired reflective layer by means of a sputtering system. For the protection of the side carrying the information structure as well as for the protection of the reflective layer applied thereto, another protective layer in the form of a protective lacquer is then applied over the reflective layer. The reflective layer must meet stringent demands with respect to faultless adhesion, adequately high reflecting properties for the laser beam reading the information, as well as retaining these properties over extended periods of time.
European Published Applications Nos. 0,064,777 Al and 0,086,009 Al have suggested the employment of metal alloys which allegedly meet the required properties for the production of the reflective layer instead of using pure metals such as silver or aluminum. Application No. 0,064,777 Al describes the use of Ag-Cu alloys with more than 40 atomic % Ag, Cu-Cr alloys with more than 8 atomic % Cr, an Al-Cr alloy with more than 75 atomic % Al, an Al-Cu alloy with more than 40 atomic % Al, an Al-B alloy with more than 70 atomic % Al, an Al-Mn alloy with at least 75 atomic % Al, and an Al-lanthanide alloy containing from 0.1 to 3 atomic % of the lanthanide.
Published Application No. 0,086,009 suggests using reflective surfaces composed of a nitride, carbide or boride of a transition metal from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, molybdenum, lanthanum, tantalum, and tungsten.